106 INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 



Shower. — A fall of rain, of sliort duration but often of cousideralile intensity, 

 and usually consisting of relatively large drops. Also a similar fall of snow, 

 sleet, or hail. Showers characteristically fall from isolated clouds separated 

 from one another by clear spaces. They occur typically in air masses that 

 posses a high degree of instability. ( See also part V. ) 



Sleet. — 1. Frozen or partly frozen rain ; frozen raindrops in the form of 

 particles of clear ice. (The official definition of the United States Weather 

 IJureau.) 2. Snow and rain falling together. (The British use, and the one 

 occurring in publications of the International Meteorological Organization. In 

 popular and engineering use in the United States the word is often applied to 

 a coating of glaze on trees, wires, rails, etc.) 



Siioic. — Precipitation in the form of small ice crystals, falling either sep- 

 arately or in loosely coherent clusters (snowflakes). (See also part V.) 



Soft hull. — White, opacpie, round pellets of snow. (See also part V.) 



Soldi' coiistaiit of fiidiatioii. — The intensity of solar radiation outside the 

 earth's atmosphere at the earth's mean distance from the sun. Recent investi- 

 gations indicate that this intensity may vary and that its mean value is l.!>4 

 gram-calories per miiuite per square centimeter of area lying normal to the 

 incident solar ray. 



Soinidiiif/ balloon. — A free, unmanned l);;ll(;on carrying a set of self-registerii;g 

 meteorological instruments. 



Source region. — An extensive area of the earth's surface characterized by 

 essentially uniform surface conditions and which is so placed in respect to 

 the general atmospheric circulation that air masses ma.v remain over It long 

 enough to acquire definite characteristic projterties. Examples of source re- 

 gions are the ice-covered polar regions and the broad expanses of uniformly 

 warm tropical oceans. 



Specter of the Bro<k<n. — The shadow of an observer and of ob,iects in his 

 immediate vicinity cast u]K)n a cloud or fog bank: sometimes attended by a 

 series of colored rings, called the glory or Brocken-bow. 



Squall. — 1. A sudden storm of brief duration: closely akin to a thunder- 

 storm but not necessarily attended by thunder and lightning. 2. A sudden 

 brief blast of wind, of longer duration than a gust. 



Stahiliti/. — A state in which the vertical distril)uti<)n of temperature is such 

 that an air particle will resist displa-.-ement from its level. In the case of 

 unsaturated air tlie lapse rate for stabilit.v will be less than the dry adiabatic 

 lapse rate; in that of saturated air less than the saturated adiabsitic lapse 

 ra te. 



Static— (Set- Stray.) 



Storm. — A markt-d disturbance in tlu> normal state of tlie atmosphei'e. The 

 term has various ajjplications. according to the context. It is most often ap- 

 plied to a disturl)ance in which strong wind is the most prominent char- 

 acteristic, and sometimes s])ecifically to a wind of force 11 on the Beaufort 

 scale. It is also used for other types of disturbance, including tliunder- 

 stoi'ms, rainstorms, snowstorms, hailstorms, dust storms, sand storms, magnetic 

 storms, etc. 



Stratiform. — A general term ai)])lied to all clouds which are arranged in 

 unbroken horizontal layers or slieets. 



Strato< tinniliis. — A form of cloud. (See])art Y. ) 



Stratosplicre. — The upjjer region or external layer of the atmosphere, in 

 which the temperature is practically constant in a vertical direction. The 

 stratosphere is free from clouds (except occasional dust clouds) and from 

 strong vertical air cui-rents, in other words, active convection. The height of 

 its base (see Tropopause) varies in regular fashion with latitude and with 

 the seasons over the earth as a whole and fluctuates irregularly from day to 

 day over any particular place. 



Stratum. — A form of cloud. (See part V.) 



Stray. — A natural electromagnetic wave in the ether. The term is used 

 in reference to the effect of such wavi> in producing erratic signals in rad'i^- 

 telegraphic receivers. Strays are also known as atnn)spherics, and collec 

 tively, as .static. 



Siih^ideiice. — The \A()rd used to denott' a slow downward motion of the 

 air over a large ai'ea. Subsidence aecomjianies divci'genrc in tiic horizontal 

 motif)n of tlie lower layers of the atmosi)liere. 



Sun pillar. — (See Light pillar.) 



Suii.^hine recorder. — An instrument for recording the duration of sunshine; 

 certain tynes also record the intensitv of sunshine. 



